Which event commonly causes an MCL injury?

• A. A twisting motion or direct blow to the inner knee.
• B. Direct blow to the outer knee.
• C. Hyperextension without contact.
• D. Overuse running without a specific incident.

Answer: (A)

The main idea is that the medial collateral ligament (MCL) is stressed by forces that push the knee inward (valgus stress). A twisting motion with the foot planted or a direct blow to the inner side of the knee both create that inward force, placing strain on the MCL and potentially tearing it. The MCL’s job is to resist those inward forces, so when they occur with sufficient force, an injury can result.

In contrast, a blow to the outer knee tends to produce lateral-side stress and often implicates the structures on the outside of the knee rather than the MCL. Hyperextension without contact more commonly injures the ACL or other structures due to forced straightening, and overuse running without a specific incident points to tendinopathy or overuse injuries rather than an acute ligament tear.